When Mina Richards chases soccer balls along the western edge of Golden Gate Park, she sprints through grass - and around gopher holes.

In the absence of field lights, the 16-year-old's practices end with the sun.

But those elements of the Beach Chalet Athletic Fields would change under a proposed renovation seeking the city's approval.

The 9.4-acre sports facility currently consists of four grass fields surrounded by a chain-link fence, a parking lot with 50 spaces, a restroom building and a maintenance shed.

Under a proposed construction backed by a public-private partnership, synthetic turf would replace the grass. The fields and the parking lot would be expanded. Field lights, benches for players, bleachers for 1,000 spectators, a barbecue area and a community room would be installed. The restrooms would be redone.

Built more than 75 years ago and last updated in 1998, the fields badly need repair, the project's proponents say.

"I have to constantly think about the ground, making sure there are no holes or anything," said Mina, a center midfielder who has been playing at Beach Chalet for 10 years with various nonprofit leagues.

The fields are currently closed Mondays, after sundown and up to four months a year to allow the grass to grow. In addition, one of the four fields is usually closed to allow for field maintenance. In its renovated form, the whole facility would be open year-round until 10 p.m., or an extra 9,600 hours.

The city's Recreation and Park Department and the nonprofit City Fields Foundation are sponsoring the project, which is estimated to cost between $12 million and $15 million.

"We have a shortage of ball fields, and it's critically important to San Francisco's families that we give our kids a place to play," said Phil Ginsburg, general manager of the Recreation and Park Department.

But the project has drawn scrutiny from neighboring environmentalist groups. They say the 10 60-foot-tall field lights will ruin the natural darkness enjoyed by those who stroll there after sunset.

"The character of the ocean and the beach and what people go out there for, to enjoy natural beauty, will be completely changed by this project," said Katherine Howard, a member of SF Ocean Edge, a grassroots group against the construction. Other opponents include the Golden Gate Park Preservation Alliance and the Golden Gate Audubon Society.

The project's draft environmental impact report, a state-required document, says the light emitted is not expected to significantly harm views of the area.

"We don't think plastic grass is any more appropriate than plastic trees or little rubber birds up in the trees," Howard said. "It's a park. It should be an ecosystem. It should be living and growing."

But grass cannot be maintained year-round, which makes turf the best alternative, said Patrick Hannan, director of communications, planning and programs for the City Fields Foundation.

"If you're going to put grass on an athletic field, you're going to restrict public access, which means you're going to turn kids away," he said.

The public money for the construction would come from a $185 million bond passed in 2008 to renovate several city parks and playgrounds. So far, the City Fields Foundation and the Recreation and Park Department have renovated six facilities, with three to go.

The Planning Commission held a hearing on the project's draft environmental impact report in early December. City planners are now working on the final version of the analysis. If approved, construction would last about 10 months.